1. Field of the Invention
The present invention relates to a magnetic tape cartridge or cassette having a rigid or resilient belt driving means. A magnetic tape cartridge is commonly referred to as a "cassette" and these terms as used herein are intended to mean the same thing.
2. Description of the Prior Art
Typical tape cartridges utilize tape which is 0.156 inches wide. Such tape is capable of storing only a limited amount of information. Recent tape recorders have been developed which require a tape cartridge which is capable of storing a much larger amount of information, as much as 120,000 bits per inch. To store this amount of information, it has been proposed to use tape as wide as a quarter of an inch.
Recent video cassette recorders also require that the tape be transported at a relatively fast rate so that the desired amount of information can be adequately recorded and played back. Typical digital recording tape is generally 60 feet long and provides 15 minutes of playing time. However, recent video recorders require as much as 300 feet of tape in order to provide 20 minutes of playing time. If such a long tape is to be used in a small cartridge, the tape must be extremely thin so that the size of the supply and take-up reels can be kept reasonably small.
Problems have been encountered in constructing a cartridge capable of transporting such a wide and thin tape. The tape tends to bounce in the vertical direction as it is transported past the machine heads. Tape bounce causes errors in recording and reading the tape especially when high recording densities are being used. There have been attempts in prior art cartridges to minimize tape bounce by utilizing a resilient belt which turns the periphery of the take-up reel at a faster rate than the periphery of the tape supply reel is turned, thereby applying tension to the tape. FIGS. 1 and 2 show two such prior art cartridges.
In FIG. 1, a resilient belt 8 is driven in the direction of arrows 30 by a roller 26 which is driven by a recording machine drive wheel 28. The belt 8 passes around a periphery 34 of a supply reel 6, around idlers 41 and 42, and around a periphery 32 of a take-up reel 4. The belt 8 is caused to stretch by the force applied by the roller 26, and the belt 8 stretches more in the vicinity of the periphery 32 of the take-up reel 4 than in the vicinity of the periphery 34 of the supply reel 6 since the tension of the belt continuously diminishes along its length. The tension is at minimum in a section of the belt located immediately to the left of the roller 26. Therefore, since the belt 8 stretches more in the vicinity of the periphery 32 than in the vicinity of the periphery 34, the periphery of the take-up reel tries to turn faster than the periphery of the supply reel thereby applying tension to the tape 12 as it is transported past the machine heads 33. The prior art cartridge shown in FIG. 2 is similar to that shown in FIG. 1 except that a floating idler 40 is used to guide the belt instead of the fixed dual idlers 41 and 42 shown in FIG. 1.
The prior art cartridges have been found to be inadequate when a wide thin tape is utilized. Specifically, the tension supplied to the tape is insufficient to reduce the tape bounce to the degree required when very high recording densities are applied to the tape.
An improved tape cartridge as shown in FIG. 3 has been proposed and is disclosed and claimed in commonly assigned U.S. patent application Ser. No. 307,147, filed Sept. 30, 1981. The cartridge 3 has a resilient belt 8 which supports the tape 12 in the vicinity of the machine heads 33 in addition to turning the periphery of the take-up reel 4 and the supply reel 6. Again, as in the cartridges shown in FIGS. 1 and 2, the periphery 32 of the take-up reel 4 tries to turn faster than the periphery 34 of the supply reel 6 thereby applying tension to the tape as it is transported past the machine heads.
A feature common to each of the cartridges shown in FIGS. 1-3 is that the resilient belt 8 applies a non-uniform tension to the tape 12 since the resilient belt is temperature and humidity sensitive. Changes in belt tension caused by changes in temperature and/or humidity adversely affect the tension in the tape 12 as it is being transported, thereby resulting in undesirable tape bounce. Changes in the tension applied to the tape 12 also contribute to tape breakage, tape stretch and tape wear.